High purity hydrogen bromide is an important industrial raw material. Various industrial bromination processes produce gaseous by-product HBr streams or mixtures contaminated with gaseous bromine. Such streams or mixtures may also be contaminated with various organic impurities. Recovery of the HBr in highly purified form (e.g. about 98% or above and desirably about 99% or above as determined by GC) for reuse as a raw material is important both from economic and environmental standpoints. Additionally, it is of importance to remove the bromine to protect equipment such as anhydrous HBr compression systems from corrosion caused by bromine.
In commercial-scale industrial operations, it is advantageous to minimize the size of a contacting vessel for scrubbing bromine from HBr due to the demanding corrosion environment. In operations where a relatively small quantity of a gaseous mixture of HBr and bromine is available for processing, average residence time (i.e., the time the gaseous mixture and the liquid scrubber composition are in contact with each other) is of little, if any, concern. On the other hand, in plant operations where a continuous relatively large volume of gaseous mixture of HBr and bromine is available for processing, average residence times within a scrubbing vessel for removal of bromine is of considerable importance. The average residence time must be kept short in order to enable such continuously evolving relatively large volumes of the gaseous mixture to be suitably processed to remove the bromine content.
Heretofore, diphenyl oxide has been used as a scrubbing medium scrubber for removing bromine from gaseous mixtures of HBr and bromine. The resulting partially-brominated diphenyl oxide was then available for conversion to decabromodiphenyl oxide, a commercially available and versatile flame retardant used in many plastic systems. Given the stated intention of the producers of decabromodiphenyl oxide to cease production of this material, this purification route will no longer be economically attractive. In addition, the continued availability of diphenyl oxide currently appears questionable, as diphenyl oxide producers begin developing alternate outlets. Prior to this invention no equally effective and equally attractive substitute for diphenyl oxide has been known to exist. Therefore, the problem has arisen to see if it is possible to develop a new, effective, economically and environmentally attractive method for removing bromine from gaseous mixtures comprising HBr and Br2, especially those in which (i) the amount of HBr predominates over the amount of Br2 in the gaseous phase, (ii) where in many cases small amounts of other impurities are present in the gaseous mixture, and (iii) in operations where relatively short average residence times are to be used. It is believed that the present invention provides a solution to this problem that meets most if not all of the foregoing criteria.